By default Kate is trying to open and save files starting in the ~/Documents folder. While this may be convenient for some, I’d like to change it. Try as I might I couldn’t find this option in the configuration of Kate. I remember this was an option, and it was removed. Then it was a command line option but kate –help-all shows it as been removed.
The only I found to change this is via KDE > System Settings > Account Details > Paths > Document Path:
Changing that to your desired directory works fine.